KR20210033063A - Scanning in angle-resolved reflectometry and algorithmically eliminating diffraction from optical metrology - Google Patents

Abstract

A coherent light source; Scanning the target pattern using a spot of coherent light from the light source to calculate the realization of the light distribution in the collection pupil-the spot covers a part of the target pattern and the scanning is performed optically or mechanically according to the scanning pattern. -An optical system configured to be; An angle-resolved reflectometer and reflectance measurement method including a processing unit configured to generate a composite image of a collection pupil distribution by combining pupil images is provided. A measurement system and method for reducing diffraction errors by quantitatively calculating the functional dependence of the measurement parameter on the aperture size and deriving a correction term for the measurement parameter related to the measurement condition from the identified diffraction component of the functional dependency on the aperture size is provided. do.

Description

[SCANNING IN ANGLE-RESOLVED REFLECTOMETRY AND ALGORITHMICALLY ELIMINATING DIFFRACTION FROM OPTICAL METROLOGY}

Cross-reference of related applications

This application claims priority to U.S. Provisional Patent Application No. 61/664,477 filed on June 26, 2012 and U.S. Provisional Patent Application No. 61/764,435 filed February 13, 2013. The entirety of which is incorporated herein by reference.

Technical field

The present invention relates to the field of measurement of semiconductor devices and angle-resolved reflectance measurement, and more particularly, to improving accuracy and reducing noise by removing the aperture diffraction effect in the angle-resolved reflectance measurement.

Angle-resolved reflectometry is a technique used to measure parameters such as the overlay and critical dimensions of a test pattern printed on a wafer. A cone of light is focused on the test pattern and the reflectance of the pattern is collected in the pupil image as a function of the angle of incidence. The exact intensity distribution of light in the collected pupil relative to the intensity distribution in the illuminated pupil provides the information necessary to extract precise measurements of the test pattern parameters.

As target sizes become smaller due to cost and productive constraints, applying angle-resolved reflectance measurements has always become a challenge. Features constituting the test pattern are not uniform throughout the test pattern. Features always include imperfections such as edge roughness, variable line width and sidewall slope mismatch. This incompleteness of the test pattern feature scatters or reflects light in a way that changes the phase and intensity distribution of the light collected by the reflectometer.

The wafer optical metrology tool includes finite sized apertures in the field plane and pupil plane. For example, FIG. 6 is a high level schematic diagram of a metrology optical system 90 according to the prior art. 6 shows an optical fiber 91 as a light source for inspecting the wafer 80 by the pupil image sensor 94. In this particular example, light travels through the illumination pupil opening 95A, the illumination field opening 95B, the objective pupil opening 95C and the collection field opening 95D.

These openings may or may not be apodized and have the following simple purpose when placed in a plane perpendicular to the plane in which the measurement is made. The light reaching the detector (the detector placed in the field plane or the detector placed in the pupil plane) is outside the metrology target and contains signals from scattering and diffractive elements that contaminate the sort of ideal signal. One of the purposes of such aperture stop is to block out such contaminating light. For example, when the signal is collected in the pupil plane, a small aperture placed in the field plane of the collection arm, called the collection field stop, blocks light from outside the proximity of the metrology target.

As the aperture becomes smaller, the filtering (done in the field plane or pupil plane) becomes more restrictive, and the aforementioned contaminating light is removed in a more efficient manner. However, this causes diffraction. Specifically, when the size of the aperture approaches the spatial interference length of the radiation, diffraction from the aperture edge transforms the signal to a significant magnitude and affects the metrology performance. In addition, prior art methods reduce the spot size (achieved, for example, by pupil apodization done in illumination) and/or the visual field aperture size or shape and the corresponding fair choice of the collection detector. By selecting an area, diffraction from the field stop is suppressed to reduce the diffraction effect (this may be the case where larger spot ringing occurs in a certain area of the detector).

An aspect of the present invention is a coherent light source; Scanning the target pattern using spots of coherent light from the light source to calculate a plurality of light distribution realizations in the collected pupil-the spot covers a portion of the target pattern and the scanning is performed by the scanning pattern. An optical system configured to be performed according to; An angle-resolved reflectometer comprising a processing unit configured to generate a composite image of the collection pupil distribution by combining the plurality of light distribution realizations in the collection pupil is provided.

An aspect of the present invention includes the steps of quantitatively estimating a functional dependency of at least one measurement parameter on the size of at least one aperture in a metrology system; Identifying at least one diffractive component of the functional dependency related to the size of at least one aperture; A correction term for the at least one measurement parameter is derived from the at least one identified diffraction component, with respect to the measurement condition including a specific size of at least one aperture that causes a diffraction error in at least one measurement parameter. Deriving; A method comprising the step of computing the diffraction error by applying the derived correction term to the at least one measurement parameter is provided.

The above-described, additional and/or other aspects and/or advantages of the present invention are described in the following detailed description so as to be inferred from that detailed description and/or learnable by the practice of the present invention.

In order to better understand the embodiments of the present invention and to show how to practice the present invention, reference is now made to the accompanying drawings, which are merely illustrative, in which the same reference numerals refer to corresponding elements or sections throughout the drawings. Represents.
1 is a high level schematic diagram showing an angle-resolved reflectometer with optical scanning, in accordance with some embodiments of the present invention.
2 is a high level schematic diagram showing an angle-resolved reflectometer implementing a scanning pattern, in accordance with some embodiments of the present invention.
3 is a high level schematic diagram showing scanning patterns with different sizes and densities, in accordance with some embodiments of the present invention.
4 is a high level schematic block diagram showing various parameters and controlled variables of a scanning angle decomposition type reflectometer according to some embodiments of the present invention.
5 is a high level schematic flow diagram illustrating a method of measuring angle-resolved reflectance, in accordance with some embodiments of the present invention.
6 is a high level schematic diagram of a metrology optical system according to the prior art.
7 is a high level schematic diagram of a general dependency of some measurable variables, termed ^{"Quantity raw} ", in the aperture size in the system, in accordance with some embodiments of the present invention.
8 is a high level schematic flow diagram illustrating a method of algorithmically removing diffraction from optical metrology, in accordance with some embodiments of the present invention.
9 is a high level schematic block diagram showing a metrology system in accordance with some embodiments of the present invention.
10A is a schematic diagram illustrating an example of how the inaccuracy of a scatterometer overlay measurement depends on the size of a collection field stop, in accordance with some embodiments of the present invention.
10B is a schematic diagram illustrating an example of how the inaccuracies of scatterometer overlay measurements depend on the size of the collection field stop for two different values of the true overlay, in accordance with some embodiments of the present invention.
11A is a schematic diagram showing an example of how a correction method using a first type of correction reduces overlay measurement errors, according to some embodiments of the present invention.
11B is a schematic diagram showing an example of how a correction method using a second type of correction reduces overlay measurement errors, according to some embodiments of the present invention.

Before making the detailed description, it will be helpful to explain the definitions of certain terms used below.

The term “target” or “measurement target” as used herein refers to any structure used for metrology needs. The target may be part of any layer in a lithographic process, and the target may comprise different structures of the same layer or different layers.

As used herein, the term "speckle pattern" or "speckle" refers to an intensity pattern of an optical signal generated by interference of at least two wavefronts, and measurement resulting from an interfering wavefront in the sensor plane in general. It refers to the source of the error.

Referring now to the drawings, the drawings are shown merely by way of example for the purpose of describing preferred embodiments of the present invention, and provide embodiments believed to be the most useful and readily understood depictions of the principles and conceptual aspects of the present invention. In this regard, the structural details of the present invention are not shown in more detail than is necessary for a basic understanding of the present invention, and the description according to the drawings shows how some forms of the present invention are practically implemented by those skilled in the art. Will make it clear to you.

Before describing at least one embodiment of the present invention in detail, it is to be understood that the present invention is not limited in its application to the details of the configuration and arrangement of components disclosed in the following description or illustrated in the drawings. The present invention can be applied to other embodiments, or can be implemented or implemented in various ways. In addition, it should be understood that the phraseology and terminology used herein is for the purpose of description and is not to be regarded as limiting.

1 is a high level schematic diagram showing an angle-resolved reflectometer 120 with optical scanning, in accordance with some embodiments of the present invention. 2 is a high level schematic diagram showing an angle-resolved reflectometer 120 implementing a scanning pattern 128, in accordance with some embodiments of the present invention.

The angle-resolved reflectometer 120 according to the embodiment of the present invention includes the coherent light source 86 and the light source ( And an optical system 125 configured to scan the target pattern 82 using the spot 83 of coherent light from 86. In an embodiment, the difference between the light distribution realizations in the collection pupil is a result of speckle and noise, which can be identified and eliminated by comparing realizations. The spot 83 covers a part of the target pattern 82 and the scanning is performed according to the scanning pattern 128 (described later with reference to FIG. 3). The scanning is performed by moving the target pattern 82 in relation to the objective lens 89 of the optical system 125 (e.g., by moving the objective lens 89 in relation to the wafer with the target 82 or the wafer It can be performed mechanically (by moving 80 in relation to the objective lens 89), or the scanning can be performed optically by changing the beam path of the illumination spot (described later). The reflectometer 120 also includes a processing unit 130 configured to generate a composite image of the collection pupil distribution by combining a plurality of light distribution realizations (ie, pupil images) in the collection pupil. For example, the collection pupil may be the pupil of the objective lens 89.

In an embodiment, reflectometer 120 focuses spatially coherent illumination to a smaller spot than can be achieved with spatially incoherent illumination. The angle-resolved reflectometer 120 may support a smaller test pattern than the reflectometer 120 using spatially incoherent illumination by using spatially coherent illumination. The coherent light source 86 may comprise a laser source capable of generating bright spatially coherent illumination that provides sufficient illumination for an angle-resolved reflectometer. Such illumination avoids a high level of shot noise caused by insufficient brightness of the light source, which is spatially incoherent.

3 is a high level schematic diagram showing scanning patterns 128 with different sizes and densities, in accordance with some embodiments of the present invention. For example, FIG. 3 shows a scanning pattern 128A on the left that is relatively dense and produces relatively low noise but has the longest measurement time. Fig. 3 shows a scanning pattern 128C on the right, which is relatively rare and small and generates relatively high noise, but has the shortest measurement time. Scanning pattern 128B is intermediate between 128A and 128C in terms of size, noise level, and scan duration.

In an embodiment, the parameters of the scanning pattern 128 and spot 83 may be configured to optimize the measured parameter and reduce errors arising from imperfections of the test pattern feature. Adjustment of the parameters of the scanning pattern 128 and spot 83 may be performed prior to operation as a calibration procedure, or during measurement as a dynamic measurement procedure.

The impact of such an error can be reduced by illuminating a larger area of the test pattern 82 with a larger spot 83 and capturing the reflected light from the larger area. In this way, the impact of the imperfections of the target 82 is reduced by averaging. Although only relatively small spots 83 in the test pattern 82 can be illuminated by using spatially coherent illumination, by moving the wafer 80 relative to the focused spot 83, the test pattern 82 is further reduced. Large areas can be illuminated. The wafer scan can be performed during the time it takes for the system sensor to capture one light distribution image in the pupil, or a continuous image can be captured when another target area is illuminated. When a continuous image is captured, the images can be combined to represent an average image of the light distribution in the pupil. Transformation of the wafer 80 to move the spot 83 on the target 82 is one possible implementation. A similar implementation consists of transforming the objective lens 89 with respect to the target 82 and wafer 80 so that the focusing spot 83 transforms in the test pattern 82.

1 shows an embodiment in which the scanning is performed optically (ie, without physical relative movement of the lens 89 and target 82) rather than mechanically. In this example, optical scanning can be performed by tilting the tiltable mirror 129 in the optical system 125 (this is a non-limiting example of optical scanning), whereby the speckle error in the optical path as described later. Can be reduced.

When a spatially coherent beam propagates through the optical system 125, the light scattered by the imperfections of the optical component propagates along with the original beam (from source 86) as an additional coherent wavefront. In the sensor plane (of detector 87), the initial beam interferes with the scattered wavefront and generates speckles in the image. Small changes in the position or pointing of the original beam can sufficiently change the relative position and angle of the scattered wavefront so that the resulting speckle pattern is wholly or partially uncorrelated with the original speckle pattern. This same motion in the original beam can be small enough so that its properties in the imaging sensor are essentially invariant. While not wishing to be bound by theory, if multiple speckle patterns are generated within the acquisition time of the imaging sensor 87, the size of the residual speckle of the image is reduced through averaging of many uncorrelated speckle patterns. It is also possible to acquire successive images each with a different beam orientation and an uncorrelated speckle pattern. These successive images can be averaged with the resulting effect of reducing the size of the residual speckle in the image. Changing the position of the spatially coherent beam over time and summing the resulting image has a general effect of reducing the spatial coherence of the image.

In embodiments, the position and angle of the spatially coherent beam is modified using a scanning optical component 129 such as a piezo-driven scanning mirror, a resonance scanner, a rotating polygon scanner, a spinning holographic scanner or an acousto-optic deflector. Can be. System 120 controllably scans the spatial coherent beam to move the system relative to the pupil plane, scan the beam to move the system relative to the field plane, or the system moves relative to both the pupil plane and the field plane. You can scan the beam to do it. In the angle-resolved reflectometer 120, it is important to have a beam distribution that is stable in the pupil plane and has low noise. For this reason, an operation of maintaining the beam position essentially fixed in the pupil plane and scanning the beam position in the field plane is a good implementation example.

4 is a high level schematic block diagram showing various parameters and controlled variables of the scanning angle decomposition type reflectometer 120 according to some embodiments of the present invention. 4 shows the coherent light source 86, the detector 87 and the objective lens 89 of the reflectometer 125, as well as the mechanical scanning 122 (wafer 80 with the target 82) and The relative transformation motion of the objective lens 89) and parameters and properties related to the optical scanning 127 are schematically shown. The reflectometer 120 is a control configured to control the scanning pattern 128 (as described above and described later) and to control and adjust (discussed later) mechanical and optical scanning (122, 127) and their interrelationships. It may include a unit 140. The reflectometer 120 includes a processing unit 130 configured to process the images from the detector 87, generating measurements and integrated images from the processed image, and other features of the images as they are taken and processed. Feedback regarding may also be provided to the control unit 140. As explained below, such feedback may further reduce noise by additional manipulation of either or both of mechanical scanning 122 and optical scanning 127.

In an embodiment, the scanning target 82 may be implemented by synchronous optical and wafer (mechanical) scanning to yield a plurality of light distribution realizations of the collection pupil from the static spot position 83 of the target 82. These realizations may differ from each other in their respective speckles, and thus may be eliminated. The processing unit 130 may also be configured to reduce the speckle of the image using realization of the light distribution of the collection pupil from the static spot position. Scanning the beam through the optical system 125 can be utilized to reduce the speckle of the final pupil image by generating and averaging multiple uncorrelated speckle images, but at the same time the focused spot 83 Scan in a larger area of (82). This has the potential side effect of requiring a larger test pattern 82 that consumes more of the valuable area on the wafer 80. By combining the optical scan 127 and the wafer scan 122, the reflectometer 120 can be configured to reduce speckle in the image, and the spot 83 is a wafer scan ( 122) and the optical scan 127 can be held statically in the test pattern 82 by precisely synchronizing them.

In an embodiment, the scanning of the target 82 may be performed by mechanical and optical scanning that is controllatively asynchronous. The processing unit 130 may also be configured to reduce the speckle of an image using optical scanning 127 and reduce errors induced by test pattern imperfections using mechanical scanning 122. In order to scan the spatial coherent beam through the optics 125 and keep the beam static in the test pattern 82, the optical scan 127 and the wafer scan 122 may be synchronized in the angle-resolved reflectometer 120. Can, but scans can also be intentionally unsynchronized. Such controllable desynchronization allows the beam through optics 125 to reduce the size of speckles introduced into the image, while also controlling the size of the area of the test pattern 82 that is illuminated to minimize the impact of test pattern imperfections. Can be used to make it scan. The size of the optical scan 127 is set to achieve the desired speckle reduction, and the size of the wafer scan 122 unsynchronization can be set to achieve the desired averaging for the test pattern imperfections.

In an embodiment, the control unit 140 is to determine the scanning pattern 128 by balancing the level of speckle reduction achieved by the optical scanning 127 and the time spent by the mechanical scanning 122. It can also be configured. In particular, the scanning pattern 128 can be optimized to balance noise reduction and measurement time. For a given test pattern 82, the reflectometer 120 can be configured to minimize the impact of feature imperfections by scanning at the largest possible area and the most probable points within that area. The reflectometer 120 may also be configured to achieve maximum optical speckle reduction by scanning the maximum possible range within the optical system 125 and scanning at the most likely point within the scan range. However, a large, dense scanning pattern 128A (e.g., left side of FIG. 3) originating from the converting wafer 80 or from optical scanning 127 (e.g., by optical component 129). May require a relatively long time to run. It is preferable that a semiconductor measurement tool consumes as little time as possible in making a measurement. Short measurement times increase tool wafer throughput and lower the cost of ownership. There is a direct tradeoff between scan range and density and measurement time.

In embodiments, reflectometer 120 may include a dynamically programmed scanning component for performing mechanical scanning 122 and optical scanning 127. The control unit 140 may be configured to control the dynamically programmed scanning component to optimize noise, error and speckle reduction along with operating parameters such as measurement duration and accuracy.

Examples of dynamically programmable scanning components are wafer stages and tilt mirrors. They can be dynamically programmed to set their scanning range and pattern. This provides the option of modifying the specific system balance between measurement speed and noise reduction by scan range and density. Thus, the reflectometer 120 is configured for shorter scans with higher wafer throughput (e.g., similar to pattern 128C) producing lower precision results, but then higher precision at lower wafer throughput. It can be modified for long scans (for example, as indicated by pattern 128A) to produce the result of. The overall pattern 128A-C has a range of measurement precision and measurement duration that can be dynamically controlled by the control unit 140.

In an embodiment, the reflectometer 120 may implement and use the programmable scan pattern 128 for intelligent reduction of test patterns and optical noise. For example, there may be a case in which a specific region of the test pattern 82 introduces more measurement noise than other regions. In an embodiment, the processing unit 130 of the reflectometer 120 may be configured to identify high noise regions of the test pattern 82. In an embodiment, the control unit 140 of the reflectometer 120 may be configured to remove the identified high noise region from the scanning pattern 82. As another example, certain regions within the optical scan pattern 128 may introduce more noise than other regions within the optical scan. In an embodiment, the processing unit 130 of the reflectometer 120 may be configured to identify areas of high noise in the optical scan 127. In an embodiment, the control unit 140 of the reflectometer 120 may be configured to avoid the identified high noise areas during optical scanning 127.

In an embodiment, reflectometer 120 may be configured to identify the high noise regions of test pattern 82 and optical scan 127 during train mode. Test scanning pattern 128, mechanical scanning 122 and/or optical scan 127 can then be defined to avoid the high noise areas during actual measurements. This principle is applicable to wafer scan 122 only, optical scan 127 only, or a combination of wafer scan 122 and optical scan 127.

In embodiments, the scanning pattern 128 may also include a characteristic intensity distribution as a function of the scan position. The characteristic intensity distribution may be implemented by mechanical scanning 122 and/or optical scanning 127. For example, the characteristic intensity distribution may be symmetrical, but not uniform, such as a Gaussian distribution. The characteristic intensity distribution includes the shape function of the scanning pattern 128 (e.g., circle, rectangle, etc.) and/or the contour function of the scanning pattern 128 (e.g., Gaussian distribution or any other symmetrical distribution). can do. The intensity distribution can be used to improve metrology accuracy in connection with or independent of the identification of the high noise region described above.

In an embodiment, the processing unit 130 may also be configured to effect generation of a composite image by applying a weighted average to the realization of the light distribution in the collection pupil, each realization being a different optical and/or mechanical scan position. Reflects. The weighting may be determined according to the characteristic intensity distribution of the scanning pattern 128. For example, the weighting can increase any part of the intensity distribution. Therefore, the individual metrology results obtained per scan point can be combined into an analysis that yields more accurate and repeatable metrology results, although not a simple intensity average for the collection pupil configuration. The weighted average and weighting parameters can be selected to optimize the measurement results.

In embodiments, the processing unit 130 may also be configured to adapt the weighting according to at least one metrology metric, such as metrology sensitivity to the location of the spot 83.

In an embodiment, the control unit 140 is specific to the scanning pattern 128 to identify or optimize the intensity distribution (shape and function) for a specific test pattern 82, for a specific measurement stack, or according to a measurement configuration. It can be configured to control or modify the intensity distribution of. For example, different intensity distributions may be applied in a train mode, and the measurement results of the processing unit 130 may be compared to identify the optimal intensity distribution of the spot 83.

5 is a high level schematic flow diagram showing an angular resolved reflectance measurement method 200, in accordance with some embodiments of the present invention. The method 200 includes a step of scanning a target pattern using spots of coherent light to calculate the realization of a plurality of light distributions in the collection pupil (step 210), and a composite image of the collection pupil distribution by combining the plurality of collected pupil images. Generating (step 270). In an embodiment, scanning 210 may include covering portions of the target pattern by coherent spots (step 212) and/or scanning the target pattern according to the scanning pattern (step 214).

In an embodiment, the method 200 includes mechanically performing scanning (step 224), for example by moving the objective lens in relation to the wafer (step 222) or by moving the wafer in relation to the objective lens (step 224). 220).

In an embodiment, the method 200 comprises performing the scanning optically (step 230), for example by tilting the tiltable mirror in the optical path of the spot (step 232) to optically scan the target. I can.

In an embodiment, the method 200 includes synchronizing mechanical scanning and optical scanning (step 240) to yield a plurality of optical distribution realizations of the collecting pupil from the static spot position of the target, and of the collecting pupil from the static spot position. Reducing the speckle of the image using light distribution realization (step 242). Alternatively or supplementally, method 200 may include controlling asynchronous mechanical and optical scanning (step 245) to reduce speckle as well as errors introduced by test pattern imperfections.

In general, the method 200 will include adjusting the mechanical and optical scanning of the target pattern (step 250), for example by controlling the dynamically programmed scanning component (step 252) that performs mechanical scanning and optical scanning. I can.

In embodiments, method 200 may include determining a scanning pattern (step 255) by balancing the level of speckle reduction achieved by optical scanning with the time spent by mechanical scanning. In another embodiment, the method 200 includes identifying high noise regions of a test pattern (step 260) and removing the identified high noise regions from the scanning pattern (step 262), and/or in an optical scan. Identifying the high noise region (step 265) and avoiding the identified high noise region during optical scanning (step 267).

In an embodiment, the spot of coherent light has a characteristic intensity distribution, and the method 200 also includes performing the generation of a composite image (step 280) by applying a weighted average to the realization of the light distribution of the collecting pupil. can do. The weighting may be determined according to a characteristic intensity distribution of the scanning pattern (step 285). In embodiments, method 200 may also include adapting the weighting according to at least one metrology metric (step 287). In embodiments, the method 200 may also include modifying the specific intensity distribution and identifying an optimal intensity distribution (step 290) with respect to a measurement parameter, such as a particular test pattern or metrology configuration.

Advantageously, reflectometer 120 and method 200 may provide any of a number of advantages: (i) spatially coherent illumination is at a smaller spot than spatially non-coherent illumination. Because it is focused, the reflectometer 120 and method 200 can achieve a smaller test pattern 82. (ii) The reflectometer 120 and method 200 can reduce the impact of test pattern imperfections because scanning the wafer in relation to the illumination spot during image acquisition reduces the impact of test pattern imperfections through averaging. (iii) Since scanning of the beam through an optical device reduces the impact of speckle noise by averaging multiple uncorrelated speckle views during image acquisition, the reflectometer 120 and method 200 reduce the impact of optical noise. I can make it. (iv) The reflectometer 120 and method 200 can be scanned through the optics for speckle reduction while maintaining spot stop in a small test pattern by synchronizing the wafer stage operation and the optical scanning operation. Can achieve reduction of optical noise in small test patterns. (v) As the wafer step operation and the optical scan operation are unsynchronized, it is possible to scan an arbitrary optical beam through optics for speckle reduction, and since an arbitrary spot can be scanned at the target to reduce target noise, reflectance System 120 and method 200 can achieve optimization of optical noise reduction and test pattern noise reduction. (vi) Reflectometer 120 and method 200 can achieve noise reduction and optimization of measurement speed because the size and density of optical and wafer scans can be modified for a tradeoff between noise reduction and measurement speed. . (vii) Since the test pattern and the scanned area of the optics can be defined to avoid areas that introduce a high level of measurement noise, the reflectometer 120 and method 200 can be used for the test pattern and high-noise areas of the optics. Can be avoided. (viii) Reflectometer 120 and method 200 can maximize test pattern noise reduction because non-coherent illumination at the exit of the multimode optical fiber uniformly illuminates the intended area of the test pattern.

The above advantages can be achieved by various configurations of reflectometer 120 and method 200 that are capable of incorporating any subgroup of features from those described above. Embodiments of the reflectometer 120 and method 200 may combine any of the following features: (i) illuminating the sample with substantially spatial coherent illumination; (ii) using stage scanning during acquisition of measurements of a single test pattern; (iii) using optical scanning during acquisition of measurements of a single test pattern; (iv) combining stage scanning and optical scanning during acquisition of measurements of a single test pattern; (v) synchronizing the stage scanning with optical scanning so that the illumination spot remains static in the test pattern during acquisition of measurements from the test pattern; (vi) synchronizing stage scanning with optical scanning in a controlled manner so that independent scan patterns can be generated in the beams passing through the optics during acquisition of the measurements of a single test pattern and in spot motions in the test pattern; (vii) the ability to adjust the scan size and density to optimize the tradeoff between measurement noise and measurement time during acquisition of measurements of a single test pattern; (viii) Reduction of spatial coherence by scanning the laser spot at the entrance of the multimode fiber.

Advantageously, the reflectometer 120 and method 200 overcomes the following limitations of current techniques.

Because wafers are expensive to process, as much wafer area as possible should be left for functional circuitry. To this end, it is desirable to make the test pattern small so that the test pattern consumes less wafer area. In order to avoid the interaction between the measurement light and the wafer geometry surrounding the test pattern, the size of the focusing spot in the angle-resolved reflectometer should be smaller than the test pattern. The smallest possible spot can be formed by focusing a spatially coherent light beam. Spatial coherence An angle-resolved reflectometer that focuses the beam on the test pattern allows for a smaller focusing spot for a smaller test pattern and leaves more wafer area available for functional circuits. It has a potential competitive advantage over reflectometers that use less light.

In the case where the measurement of the test pattern is made with small focusing spots, the magnitude of this correction to the light distribution can cause large errors and noise in the measurement of the test pattern parameters. Angle-resolved reflectometers, which can collect information from as many test patterns as possible, have a competitive advantage in that measurement errors introduced by target imperfections can be minimized through spatial averaging.

When a spatial coherent beam propagates through an optical system, a portion of the beam is scattered by the imperfections of the optical component. This scattered light propagates with the primary beam and interferes with the primary beam to create speckles. In optical metrology systems, such as angle-resolved reflectometers, information about the test pattern is included in the reflected intensity profile of the spatial coherent beam. Speckles produced by the optical system can modulate the beam intensity in an unpredictable manner, causing errors in subsequent measurements of the test target parameters.

The reflectometer 120 and method 200 described herein can not only support the minimum possible test pattern by minimizing the size of the illumination area on the wafer, but also illuminate the test pattern area as large as necessary to minimize the impact of pattern imperfections. It is possible to minimize the measurement error introduced by the speckle generated in the optical system at the same time.

Advantageously, reflectometer 120 and method 200 provide a better solution than techniques for static spatial incoherent illumination and static spatial coherent illumination.

For static spatial non-coherent illumination: The size of a spot of spatial non-coherent light focused on the wafer can be defined by a field stop arranged in the illumination path of the optical system. By increasing the size of the field stop, the area of the illuminated test pattern can be increased and the impact of target imperfections can be reduced by effectively averaging the measurements over a larger test pattern area. The limitation of the configuration using spatial incoherent lighting arises when it is necessary to reduce the size of the test pattern. Reducing the size of the test pattern should also reduce the size of the illumination spot. This can be achieved by reducing the size of the field stop, but this causes a significant amount of light loss and an increase in spatial coherence. Therefore, an angle-resolved reflectometer using a spatially incoherent light source loses light when illuminating a small test pattern. The loss of additional light at the field of view aggravates the situation and increases the measurement error due to shot noise. The increase in spatial coherence with reducing the size of the field stop also increases the impact of the speckle from the optical system. Therefore, the angle-resolved reflectometer with static spatial incoherence illumination is optimal for measuring small test patterns, as it increases shot noise and speckle when the illumination field of view aperture is reduced to support smaller test patterns. It is not.

For static spatial coherent illumination: a spatially coherent beam can be focused on a small spot on the wafer, whereby the test pattern can also be made small. However, the small spot illuminates the local imperfections of the test pattern and does not reduce the impact of the imperfections by averaging over a larger test pattern area. Spatial coherent illumination also creates speckles in the optical system, which adds noise to the test pattern measurements. Angle-resolved reflectometers with static spatial coherent illumination can measure small test patterns, but cannot be adjusted to increase the size of the illumination path to enable averaging of test pattern imperfections and subject to speckle noise.

Therefore, the reflectometer 120 and method 200 are superior to the above two approaches.

In embodiments, method 200 may be used to implement spatial coherence reduction with multimode optical fibers. For example, embodiments of the present invention may include scanning the face of a multimode optical fiber using a spot of coherent light to yield a signal with a yield mixed mode with reduced spatial coherence. .

Large core multimode fiber can be used to transmit spatially coherent light to the measurement header. Multimode fiber acts like an extended object if other points in the fiber face are uncorrelated. Normally, a laser coupled to a multimode fiber excites only a small subset of the fiber modes. To achieve the desired uncorrelation, the laser can be configured to excite all or a wide distribution of fiber modes. No randomization is required for uncorrelatedness. Uncorrelatedness can be achieved by sequentially excitation of the modes on a long time scale compared to the coherent time. Then, the short correlation time is transformed into a short correlation length. Randomization only adds noise. Unfortunately, fiber instability will always cause some randomization. The point of adding additional randomization is that many randomizations can be quieter than less randomizations.

An approach to achieving this may be to scan the focused laser beam sideways across the fiber optic face, or to scan the fiber optic face sideways across the focused laser beam in a random or quasi-random pattern. Such scanning is similar to scanning 128 described above and can likewise be performed optically or mechanically. This scan can be performed, for example, using a fold mirror with a high-speed tip tilt actuator. If the scan is fast enough, the time-varying mode structure is averaged over the detector's integration time and results in an essentially non-coherent extension source. Another approach to randomly mixing modes is to use a voice coil or other actuator to vibrate the multimode fiber.

When performing wafer metrology, accuracy, precision and tool induced shift (TIS) rely on the ability to retrieve high reliability spectral or angular information from small metrology targets. Good metrology performance requires a method of removing the induced diffraction from the apertures described above. The present invention teaches to infer a diffraction induced signal contamination that reduces the performance of conventional measurements to a “diffraction-free” limit where the measurement performance clears the diffraction effect.

Diffraction through an aperture in a metrology system introduces discernable errors in the measurement output. Embodiments of the present invention computationally compensate for the errors by deriving a functional dependency of at least some of the errors in the aperture size. Functional dependencies can be derived for different measurement parameters, such as measurement results or measured intensity. The derivation can be carried out before the actual measurement or during the measurement (on the fly). The functional dependency can be used to calibrate the measurement system for a large aperture size combined set with respect to a plurality of apertures in the system.

The method described here also provides a margin of error for measurements induced by diffraction-related signal contamination. As shown in FIG. 6, various apertures in metrology optical system 90 can induce diffraction errors.

The diffraction effect can cause degradation of metrology performance such as accuracy, and can also cause degradation of precision due to enhanced sensitivity to focus and radiation spot alignment errors. The concepts described herein include collecting signals from multiple aperture sizes, and collectively using the information to infer data with "no diffraction limiting" where the metrology performance clears the contaminant interference effects.

This concept is schematically illustrated in FIG. 7 showing the global dependence of some measurable variable, termed ^{"Quantity raw} ", in the size of an aperture of the system 90, for example one of the minimum apertures. The measured amount of ^raw is denoted as Quantity raw, and the opening size is denoted as L. L ₁ , L ₂ , L ₃ , ..., L _n represent values obtained by L from measurement numbers 1,2,3,...n. No diffraction limit is ^raw Quantity = Quantity of ^ideal is obtained from L = ∞, the target of the method disclosed herein is _{L = L 1, L 2,} L 3, ..., L n, and L = ∞ In the ^raw Quantity By inferring the collected data for Q, we get an estimate for ^{Quantity ideal} , which can be used to correct the ^{measured Quantity raw at a given aperture size.}

Since the measurement error effect induced by diffraction behaves in a way that fluctuates as a function of L, the system and method perform a train mode so that the function Quantity ^raw (L) is smoothed and an inference for L→∞ can be made. You can choose the value of L.

This dependence of the measured variable in aperture size may be measured for different apertures in system 90 to generate a multidimensional correction matrix that references some or all apertures in system 90. The relevant openings for the analysis can be selected according to their size, or according to their influence on the resulting diffraction error. For example, the first approximation may include compensation of the diffraction effect caused by the minimum aperture. If there are two similar minimum apertures, the correction matrix can be two-dimensional.

The "quantity" deduced up to that L→∞ limit and plotted on the y-axis is one or more of a variety of possible measurement parameters, such as intensity per pixel or derived intensity (same as the differential signal in a scatterometer overlay), or ultimate. Phosphorus measurement performance (such as a CD of a layer, or, for example, an overlay between two layers as schematically shown in FIG. 10A below). Performing the extrapolation method provides an estimate of the margin of error in the measurement. For example, it is possible to perform extrapolation by two or more extrapolation techniques (eg, different forms for the extrapolation function, different intervals in L used in the interpolation method) and compare the results. The difference between the results can serve as a good estimate of the margin of error in the measurement. Embodiments of the present invention include, for example, a wheel with multiple apertures, an adjustable iris-like aperture, or a spatial light modulator (SLM) for determining and modifying _{different aperture sizes (values of L-L i ).} Any of several instruments can be used, such as electro-optical devices.

This concept is illustrated in more detail by the example shown in Fig. 10A, which is a schematic diagram showing an example of how the inaccuracy of scatterometer overlay measurements depends on the size of the collection field stop, in accordance with some embodiments of the present invention. 10A shows how the overlay measurement depends on the collection field aperture size for a given collection field aperture size L (ca. 4-23 μm range) that is fairly selected to avoid the diffraction-induced measurement error variation described above. . These results were obtained by simulation of an overlay target measured with an overlay scatterometer. Simulation results were calculated for a very large overlay target printed on a resist wafer. The true overlay of the simulated stack is equal to 16 nm, and the deviation from 16 nm is the result of misalignment errors in the illumination for the overlay scatterer target.

8 is a high level schematic flow diagram illustrating a method 300 for logarithmic removal of diffraction from optical metrology, in accordance with some embodiments of the present invention.

The method 300 includes quantitatively calculating a functional dependency of the at least one measurement parameter on the size of the at least one aperture in the metrology system (step 310); Identifying at least one diffraction component of the functional dependency associated with the size of the at least one aperture (step 320); And deriving from the at least one identified diffraction component at least one correction term for the at least one measurement parameter in relation to the measurement condition (step 330). The measurement conditions include a specific size of at least one aperture that causes a diffraction error in at least one measurement parameter. Measurement conditions may also include additional parameters such as illumination wavelength and illumination source properties (eg, spot alignment). The method 300 also includes the step of computationally compensating for the diffraction error (step 340) by applying the derived correction term to at least one measurement parameter. Hence, the method 300 corrects the measurement parameter by computationally removing the diffraction error due to the aperture size (step 342).

In an embodiment, at least one of the calculating 310, the identifying 320, the deriving 330 and the compensating step 340 may be executed by at least one computer processor 105. . In an embodiment, a computer program product is disclosed including a computer-readable storage medium having a computer-readable program stored thereon. The computer-readable program is configured to perform at least one of steps 310, 320, 330, and 340 of method 300, as well as any other steps of method 300.

In embodiments, method 300 may also include selecting an aperture size that yields a smoothing function dependency (step 311). The aperture size may be selected to yield a functional dependency that enables identification 320 and derivation 330. In an embodiment, a suitable aperture size can be selected by examining different aperture sizes in the train mode.

In embodiments, estimating step 310 may be performed by fitting the curve to the measurement according to theoretical or analytical considerations or simulation results (step 312). The identifying step 320 may then be performed using the fit curve to identify the diffraction component as a series of terms representing the fit curve, for example (step 322).

In embodiments, method 300 may include using at least one measurement result (step 314) as at least one measurement parameter including at least one measurement result. For example, the at least one measurement result may include any of an overlay measurement, a critical dimension (CD) measurement, a focus measurement, a dose measurement, a side-all angle calculation, a film thickness measurement, and the like. have.

In an embodiment, the method 300 incorporates the estimating step 310 and the identifying step 320 in the metrology measurement process to continuously monitor and, if necessary, update the correction term according to the measurements being performed on-the-fly. It may include a step (step 325).

In an embodiment, the estimating step 310 and the identifying step 320 may be performed prior to the metrology measurement process and may be used to calibrate the metrology system (step 324). In an embodiment, the method 300 may also include refining the correction value (step 345) by repeating the error calculation, e.g., by correcting the measurement measurement according to the derived correction term, as described below. . In an embodiment, method 300 includes deriving a second order correction term by repeating any of the steps of calculating 310, identifying step 320, and deriving step 330 after first order compensation 340. can do.

9 is a high level schematic block diagram showing a metrology system 100 in accordance with some embodiments of the present invention.

Metrology system 100 computationally compensates for diffraction errors associated with the size of at least one aperture 95 of metrology system 100 by applying one or more correction terms 130 to at least one measurement parameter 112, 114. Is configured to The measurement parameters are the measurement results 112, such as the critical dimension of a layer (CD) or an overlay between two layers, and/or other measurement parameters such as intensity per pixel or derived intensity (equivalent to the differential signal of the scatterometer overlay). (114) may be included. The correction term 130 quantitatively calculates the functional dependency of the measurement parameter (e.g., Figs. 7, 10A) at the size of the aperture 95 and at least one diffraction component of the functional dependency related to the size of the aperture 95 Can be derived by identifying. The metrology system 100 performs the calculation step and the identification step on-the-fly (e.g., by controlling the aperture size and measuring a parameter) and/or identifying at least one diffractive component of a functional dependency. A controller 110 (eg, having at least one computer processor 105) configured to calibrate the metrology system 100 may be included. The actual manipulation of the aperture size can be performed by any aperture size determination mechanism 115, such as a wheel with multiple apertures, an adjustable iris-like aperture, or an electro-optical device such as an SLM.

In an embodiment, the calculation of the functional dependency may be performed (eg, by a smoothing function) with respect to a selected plurality of aperture sizes that yield a functional dependency enabling identification and derivation.

In embodiments, the correction terms 130 for several apertures may be calculated independently or independently to generate a multidimensional correction matrix that references some or all of the apertures in the system 100.

In embodiments, the system 100 may also be configured to refine the computational compensation using a functional dependency to derive a second order correction term and adjust the at least one measurement parameter accordingly. In an embodiment, the system 100 may be configured to sequentially refine the results and reduce measurement errors by repeating the correction process to compensate for other errors.

In an embodiment, the calculating step (step 210) may include fitting a curve as L→∞ for the functional dependency ^{of Quantity raw at the aperture size L (e.g., theoretical, analytical or simulation results} On the basis of). Then, we can calculate ^{the Quantity ideal} using the fit parameter. For example, if the functional dependency is expressed in Equation 1: Quantity ^raw (L) = A + correction (L) (where correction (L) = B/L ^q1 + C/L ^q2 + D/L ^q3 + ... , And 0<q1<q2<q3<...), since Quantity ^ideal ≡ Quantity ^raw (L→∞) = A, the ultimate measurement result will be A. In that case, the compensation step (step 240) is measured measurement Quantity ^raw (L) suitable for Quantity ^raw (L) by the parameter includes a step of simply replaced with "A", in which the L → ∞ "non-diffraction "Infer with limits. This procedure requires the measurement ^{of the Quantity raw} (L) for at least two L values chosen fairly as described above (Fig. 7).

If the function correction (L) and equivalently the coefficients (B, C, D, ...) represent an approximate universal dependence of the system parameters (this is better than the deviation of CD from nominal CD and wafer metrology such as overlay). This means that it depends much more strongly on wavelength, polarization, illumination contour, etc.), the following calculation procedure can be used.

The function correction (L), or coefficients (B, C, D, ...) that equivalently define the function correction are first determined. The coefficients can be accurately fixed in train mode (by using multiple L values, and by increased light level/measurement time). This secures the functional dependency of the Quantity ^raw (L) on the L, and on-the-fly correction of Quantity ^raw (L) by using a measurement value of Quantity ^raw (L) on a single L value and the accurate estimate of Quantity ^ideal To reach. For example, if you do a train measurement and know that C, D, ... can be ignored as a good approximation, but B is a non-negligible function of the tool-only parameter, At a given value of L, the following method (Equation 2): Measurement performance = Quantity ^raw (L) → Measurement performance = Quantity ^raw (L)-The measurement performance can be corrected by replacing the measurement performance with ^{B/L q1.} That is, the systems and methods can identify the non-negligible terms of the correction function and their dependency types in the system parameters, and correct the measurements only by the non-negligible terms with respect to their dependencies on the system parameters.

The above assumptions for the universal behavior of the function "correction (L)" are very reasonable, and because the measurement performance has a very weak effect on the diffraction (for example, the deviation or overlay of the CD value from the nominal CD) simulation (described later). Note that it is supported by For example, the overlay affects the diffraction effect in the form of a function that depends on the combination of 2π·overlay/pitch. Since the pitch is about 600 nm, the error induced by this dependency is on the order of a few percent.

Advantageously, the present invention improves the measurement accuracy by suppressing the aperture induced diffraction effect. In ^{addition to establishing Quantity ideal} , the present invention provides a method of calculating the ^{margin of error (Quantity raw} -Quantity ^ideal ), as it is one of the outcomes of the fit procedure performed at the time of measurement or in the train mode. This provides quantitative confidence in the measurements.

10A is a schematic diagram illustrating an example of how the inaccuracy of a scatterometer overlay measurement may depend on the size of a collection field stop, in accordance with some embodiments of the present invention. 10A is used below as a specific non-limiting example of how the present invention is applied to overlay metrology. In this illustrated case, “Quantity” is the overlay reported by the overlay scatterometer, “L” is the collection field aperture size, and the error in the overlay estimate is the misalignment between the grating structure being measured and the illumination spot. Is caused by.

10B is a schematic diagram illustrating an example of how the inaccuracy of scatterometer overlay measurements depends on the size of the collection field stop for two different values of the true overlay, in accordance with some embodiments of the present invention. As clearly shown in Fig. 10B, this error decreases to zero as L increases (the simulated overlay was chosen to be 16 nm in this example as shown in Fig. 10A). The value of L selected in this figure was selected according to the above description. Fig. 10b also clearly shows that the dependence of the inaccuracy of the metrology parameter (overlay in this example) is negligible since the above-described "universality" assumption is declared.

In this example, the implementation method 300 may include the following steps. First, step 312 includes fitting the data in FIG. 10A. In other words, a very good fit appears as a function of the form OVL(L) = A + 18.885/L ^p , which explains the simulation data well for p≒2.0 and A=16.027. The final metrology overlay result is then the value OVL(L→∞) = A = 16.027. This will lead to an overlay error inaccuracy of 0.027 nm (recall that the true overlay used in this exemplary simulation is 16 nm). Step 314 includes correcting the measured value using the calculated inaccuracies.

Advantageously, this fit can also be made from only the two lower field stop size values L=4.15 μm and L=7.25 μm. In such a case, the value of A is 16.215, leading to an estimate of inaccuracy of 0.215 nm (using only L=7.25 μm gives an inaccuracy of about 0.5 nm, and the result of L=4.15 μm is approximately 1.1 nm). Provides degrees).

Another way to implement method 300 is to consider the aforementioned fit as a correction to how the overlay value depends on the collection field aperture size. To demonstrate this fact, FIG. 10B also shows how the overlay inaccuracy behaves for two overlay targets, such as 0 nm and 16 nm, with overlay values of 0 nm and 16 nm. As clearly illustrated by Fig. 10B, the inaccuracy depends very weakly only on the true overlay of the stack as described above. This is a method of performing the following type of secondary calibration (step 324), i.e. (i) using the calibration formula obtained by fitting the overlay data (in the example above this formula is OVL(L) = 16.027 + 18.885/L ² ), and (ii) applying the above formula to a new overlay measurement in the following way (the new overlay measurement is denoted OVL'(L)). First, the new overlay measurement OVL'(L) is replaced with the corrected measurement: OVL'(L) → OVL'(corrected L) = OVL'(L)-18.885/L ² .

11A is a schematic diagram showing an example of how a correction method using a first type of correction reduces overlay measurement errors, according to some embodiments of the present invention. 11A shows the improvement achieved by applying a second order approximation as described above. In the example shown, the resulting error reduction by calibration is provided for the case of true overlay=0. Note that this entails a single measurement at a single value of L.

Obviously, uncorrected results cause significant overlay errors, especially in the case of small collection field aperture sizes, and the corrected results greatly reduce these errors. Note that this error can also cause a decrease in precision if the root cause of the inaccuracy (spot misalignment in this example) fluctuates over time.

11B is a schematic diagram showing an example of how a correction method using a second type of correction reduces overlay measurement errors, according to some embodiments of the present invention. The second type of calibration is carried out in the following manner. First, the overlay measurements used for calibration are denoted as OVL(L;0). For example, these may be measurements suitable for OVL(L;0) = A + calibration (L) (where A = 16.027) and calibration (L) = 18.885/L ^2. At this point, the best estimate for a true overlay of this calibration measurement is 16.027 nm. In this second type of calibration, the fact that the diffraction effect for the two overlay measurements is very weakly dependent on the actual value of the overlay is used to correct the new overlay measurements. The new overlay measurement is denoted as OVL(L;1) as follows: OVL(L;1) → OVL(corrected L;1) = OVL(L;1) + OVL(L;0)-A. degrees As shown in 11b, the second type of correction is preferred over the first type of correction in this example because it yields a more stable correction with respect to the changing field aperture size.

Note that in the above two calibration methods, it is important that the measurement conditions do not change significantly between the calibration measurement and the actual measurement. This includes the properties of the light (wavelength, polarization, alignment of the system to the target, focus, etc.). In cases where it is not possible to guarantee that the measurement conditions are the same, additional calibration may be required to correct and compensate for the difference. For example, if the overlay scattering system is misaligned along the x-axis by an amount of d with respect to a large overlay target, the overlay measurement (OVL) is a two-dimensional function that depends on the collection field aperture size (L) and d, i.e. OVL( It should be formulated as L,d). Since decentering at L→∞ causes zero inaccuracies, the function can be expressed as OVL(L,d) = A + f(d)·g(L), g(L→∞)=0. have.

In the case of two dimensions, the calibration process can be divided into the following steps. First, d is _{fixed at d 0} and OVL(L, d ₀ ) is fitted to obtain A. Correction (d,L) is defined as correction (d,L) ≡ OVL(L,d)-A, and correction (d ₀ ,L) = f(d ₀ )·g(L) is obtained. Then, the correction (d ₀ ,L) is divided by the correction (d ₀ ,L ₀ ) to obtain an estimate for the ratio r _g (L) = g (L)/g (L ₀ ).

These steps are _{repeated for various values such as d i} = d ₁ , d ₂ , d ₃ , d _{4 to obtain the correction (d i} ,L), and by dividing these results as described above (correction (d _i ,L)/correction(d _i ,L _i )), the calculation of the function r _f (d) = f(d)/f(d ₀ ) is formed. Combining the above steps with the measurements of the overlay at L=L ₀ and d=d ₀ , giving the correction (L ₀ ,d ₀ ), the estimate for OVL(L,d) is OVL(L,d) = It can be expressed as A + correction (L ₀ ,d ₀ )·r _f (L)·r _{g (d).} As a result, for any new overlay measurement OVL(L,d) performed at some values of L and d, the correction is OVL(L,d) → OVL(corrected L,d) = OVL(L,d) -It will be corrected (d ₀ ,L ₀ )·r _g (L)·r _f (d).

Accordingly, the method 300 may also include calibrating the correction term for at least one difference between the derivation condition (the condition of the metrology system 100 during derivation) and the measurement condition (step 332). The at least one difference may be related to, for example, the wavelength or polarization of the measurement beam, the alignment of the system 100 with respect to the target, a focus parameter, and the like.

In an embodiment, the method 300 provides a calibration (332) by expressing a functional dependency as relating to the at least one difference (step 334) and deriving a correction term for a range of values of the at least one difference (step 336). ).

In an embodiment, each metrology system 100 may also be configured to calibrate the correction term for at least one difference between the derivation condition and the measurement condition, the at least one difference being wavelength, polarization, alignment to target, And at least one of focus. The metrology system 100 may be configured to perform calibration by expressing a functional dependency as relating to the at least one difference and deriving a correction term relating to a range of values of the at least one difference.

In the above description, the embodiment is an example or implementation example of the present invention. The various aspects of “one embodiment”, “an embodiment” or “some embodiments” are not necessarily all referring to the same embodiment.

Although various features of the present invention may be described in connection with a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the present invention may be described herein in connection with a separate embodiment for clarity, the present invention may also be embodied in a single embodiment.

Embodiments of the present invention may include features from embodiments different from those described above, and embodiments may incorporate elements from embodiments other than those described above. The description of elements of the invention in connection with a particular embodiment is not limited to being used only in that particular embodiment.

In addition, it should be understood that the present invention may be implemented or practiced in various ways, and the present invention may be implemented in embodiments other than those described above.

The invention is not limited to the accompanying drawings or their corresponding description. For example, the flow does not have to proceed through each illustrated box or state, and does not have to proceed in the exact same order as illustrated and described.

The meanings of technical terms and scientific terms used herein have meanings commonly understood by those of ordinary skill in the art, unless otherwise defined.

Although the present invention has been described in connection with a limited number of embodiments, these embodiments should not be construed as limiting the scope of the invention, but should be understood as illustrating some preferred embodiments. Other possible changes, modifications and applications are also included within the scope of the present invention. Accordingly, the scope of the present invention is not limited to those described above, but is determined by the appended claims and their legal equivalents.

Claims (46)

Quantitatively estimating a functional dependency of the at least one measurement parameter on the size of the at least one aperture in the metrology system;
Identifying at least one diffractive component of the functional dependency associated with the size of at least one aperture;
A correction term for the at least one measurement parameter is derived from the at least one identified diffraction component with respect to a measurement condition including a specific size of at least one aperture that causes a diffraction error in at least one measurement parameter. Deriving;
Computing the diffraction error computationally by applying the derived correction term to the at least one measurement parameter,
Wherein at least one of the calculating, identifying, deriving and compensating is performed by at least one computer processor. The method of claim 1, further comprising selecting a plurality of aperture sizes for performing a quantitative estimation of the functional dependency, wherein the aperture size is selected to calculate a functional dependency enabling the identification and the derivation. Way. The method of claim 1, further comprising calibrating metrology measurements according to the derived correction terms. 4. The method of claim 3, further comprising repeating the calibration to refine the calibration term. The method of claim 1, further comprising deriving a second order correction term by repeating the calculating step and the identifying step after the compensating step. The method of claim 1, wherein the step of estimating the functional dependency is carried out by curve fitting, and the step of identifying is carried out in relation to a curve parameter. The method of claim 1, wherein the at least one measurement parameter comprises at least one measurement result. The method of claim 7, wherein the at least one measurement result comprises at least one of an overlay measurement, a critical dimension measurement, a focus measurement, a dose measurement, a side-wall angle calculation, and a film thickness measurement. The method of claim 1, further comprising calibrating the correction term with respect to at least one difference between derivation conditions and measurement conditions. The method of claim 9, wherein the at least one difference is related to at least one of wavelength, polarization, alignment to the test pattern, and focus. 10. The method of claim 9, wherein the step of correcting is performed by expressing the functional dependency as related to the at least one difference and deriving the correction term in relation to the range of values of the at least one difference. The method of claim 1, wherein the calculating and identifying are integrated in a metrology measurement process. The method of claim 1, wherein the calculating and identifying are performed prior to a metrology measurement process and are used to calibrate the metrology system. At least one correction term derived by quantitatively calculating the functional dependency of at least one measurement parameter with respect to the size of at least one aperture and identifying at least one diffraction component of the functional dependency related to the size of the at least one aperture A metrology system arranged to computationally compensate for a diffraction error associated with the size of the at least one aperture in the metrology system by applying to a measurement parameter. 15. The metrology system of claim 14, wherein the calculation of the functional dependency is performed in relation to a selected plurality of aperture sizes that yield a functional dependency enabling the identification and derivation. 15. The metrology system of claim 14, further comprising a controller arranged to perform the calculation and the identification on the fly. 17. The metrology system of claim 16, wherein the controller is arranged to calculate the functional dependency by curve fitting and to identify at least one diffraction component relative to a curve parameter. 17. The metrology system of claim 16, wherein the controller is arranged to control the aperture size by an aperture size determination mechanism. 15. The metrology system of claim 14, wherein the metrology system is calibrated according to identifying at least one diffractive component of the functional dependency. 15. The metrology system of claim 14, wherein the metrology system is further arranged to refine the computational compensation using the functional dependency to derive a second order correction term and adjust the at least one measurement parameter accordingly. The method of claim 14, wherein the metrology system is further arranged to correct the correction term in relation to at least one difference between derivation conditions and measurement conditions, the at least one difference being wavelength, polarization, alignment to the test pattern. , And focus. 22. The metrology system according to claim 21, arranged to perform said calibration by expressing said functional dependency as being related to said at least one difference and deriving said correction term in relation to a range of values of said at least one difference. A computer program product including a computer-readable storage medium having a computer-readable program embedded therein,
The computer-readable program,
A computer-readable program configured to quantitatively estimate a functional dependency of the at least one measurement parameter on the size of the at least one aperture in the metrology system;
A computer readable program configured to identify at least one diffractive component of the functional dependency associated with the size of at least one aperture;
A computer configured to derive a correction term for the at least one measurement parameter from the at least one identified diffraction component with respect to a measurement condition including a specific size of at least one aperture causing a diffraction error in at least one measurement parameter. A readable program;
And a computer readable program configured to computationally compensate the diffraction error by applying the derived correction term to the at least one measurement parameter. 24. The computer program product of claim 23, wherein the calculation of the functional dependency is performed by curve fitting and the identification is performed in relation to a curve parameter. 24. The computer program product of claim 23, further comprising a computer readable program configured to refine the computational compensation using the functional dependency to derive a second order correction term and adjust the at least one measurement parameter accordingly. The method of claim 23, further comprising a computer-readable program configured to calibrate the correction term in relation to at least one difference between derivation conditions and measurement conditions, wherein the at least one difference is for wavelength, polarization, and test pattern. Alignment, and at least one of focus, and the computer-readable program further expresses the functional dependency as related to the at least one difference and calculates the correction term in further relation to a range of values of the at least one difference. A computer program product configured to perform the calibration by deriving. In the angle-resolved reflectometer,
Coherent illumination source;
A controller including one or more processing units;
An optical system arranged to scan a test pattern of a sample, with a spot of coherent light from the coherent illumination source, the scan being configured to have an adjustable scan size and density, the scan being performed according to the scanning pattern, the The scanning pattern causes the spot to be scanned across the test pattern, and the optical system comprises a scanning mirror configured to control the position of the spot of coherent light;
A detector configured to collect reflected light from the test pattern of the sample to produce a plurality of pupil images of a light distribution in a collection pupil; And
And a processing unit configured to generate a composite image by combining two or more of the plurality of pupil images of the light distribution collected in the collecting pupil. 28. The angular resolved reflectometer of claim 27, wherein the scanning mirror is configured to position the spot of the coherent light on the sample during an overlay measurement. 28. The angular resolved reflectometer according to claim 27, wherein the processing unit is further configured to control the scanning mirror. 30. The angle-resolved reflectometer of claim 29, wherein the processing unit is further configured to identify an optimal intensity distribution and correct the light distribution with respect to a specific test pattern or metrology configuration. 28. The angular resolved reflectometer of claim 27, wherein the processing unit is further configured to identify high noise regions of the test pattern. 32. The angular resolved reflectometer of claim 31, wherein the processing unit is configured to remove the identified high noise area of the test pattern from the scanning pattern. 28. The angular resolved reflectometer of claim 27, wherein the processing unit is further configured to identify an identified high noise area of the test pattern in an optical scan. 34. The angular resolved reflectometer of claim 33, wherein the processing unit is configured to avoid an identified high noise area of the test pattern during the optical scan. 28. The angle-resolved reflectometer of claim 27, wherein the scanning pattern comprises a symmetrical and non-uniform light distribution. In the angle-resolved reflectance measurement method,
Directing a spot of coherent light, wherein the spot of coherent light is smaller than the size of the test pattern, at a test pattern, using a scanning mirror;
Using the scanning mirror, scanning the test pattern with a spot of coherent light to yield a plurality of pupil images of light distribution in the collecting pupil-the scanning means that the spot is scanned across the test pattern Is executed according to the scanning pattern, and the scan size and the scan density of the scanning pattern are adjustable;
Using a detector, collecting light reflected from the test pattern to produce a plurality of test pattern images; And
Using one or more processing units to generate a composite image of the collected pupil light distribution by combining two or more of the plurality of pupil images of the light distribution in the collecting pupil. . The method of claim 36,
Using the scanning mirror to position a spot of coherent light on the sample during overlay measurement. The method of claim 36,
Identifying a high noise region of the test pattern; And
And removing the identified high noise area of the test pattern from the scanning pattern. The method of claim 36,
Identifying areas of high noise in the optical scan; And
Avoiding the identified high noise regions of the test pattern during the optical scan. 37. The method of claim 36, wherein the scanning pattern comprises a specific intensity distribution. The method of claim 36,
And scanning the test pattern using one or more processing units to control the configuration of the scanning mirror. The method of claim 36,
And reducing speckle in the composite image using a plurality of pupil images of a light distribution collected in the collection pupil from a static spot location. The method of claim 36,
Further comprising the step of scanning the test pattern using a scanning pattern including a symmetrical and non-uniform light distribution, angular decomposition type reflectance measurement method. The method of claim 36,
Identifying an optimal intensity distribution and modifying the light distribution with respect to a particular test pattern or metrology configuration. 28. The angular resolved reflectometer of claim 27, wherein the processing unit is further configured to reduce speckle in the composite image using a plurality of pupil images of a light distribution in the collecting pupil. 28. The angle-resolved reflectometer of claim 27, wherein the coherent illumination source is a laser.

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